In recent years, there are increasing needs for a flat panel display in accordance with advancement of a highly information-based society. Known as the flat panel display are a non-self-luminous liquid crystal display (LCD), a self-luminous plasma display (PDP), an inorganic electroluminescence (inorganic EL) display, an organic electroluminescence (organic EL) display, etc. Above all, advancement of organic EL displays is especially remarkable.
As for organic EL displays, a technique of displaying a moving image according to simple matrix driving and a technique of displaying a moving image according to active matrix driving of organic EL elements with the use of thin-film transistors (TFTs) are known.
In a conventional display, a pixel emitting red light, a pixel emitting a green light, and a pixel emitting a blue light are aligned as a single unit so as to create various colors represented by white. A full-color image is thus displayed.
In the case of organic EL display devices, this is achieved generally as follows. Specifically, red, green, and blue pixels are formed by creating a color pattern on an organic light emitting layer by a mask deposition method using a shadow mask. However, this method faces the challenges of mask processing accuracy, mask alignment accuracy, and an increase in mask size. Especially, in the field of large-sized displays represented by televisions, the substrate size is becoming larger and larger (from G6 to G8 and to G10). The conventional method requires a mask having a size equivalent to or larger than the substrate size, and therefore requires production and processing of a mask corresponding to a large-sized substrate. However, since a mask requires a very thin metal (general film thickness: 50 nm to 100 nm), it is very difficult to increase the mask size. As such, production and processing of a mask corresponding to a large-sized substrate become problems. The problems of mask processing accuracy and mask alignment accuracy lead to mixture of colors caused by mixture of light-emitting layers. In order to prevent this problem, it is generally necessary to increase a width of an insulating layer provided between pixels. This reduces the area of a light-emitting section in a case where the area of the pixels is fixed. This leads to a decline in aperture ratio of the pixels, thereby leading to a decline in luminance, an increase in power consumption, and a decline in lifetime. Further, according to a conventional production method, a deposition source is disposed below a substrate, and an organic layer is formed by depositing an organic material in an upward direction. This causes a problem of flexure in a central part of a mask as a result of an increase in substrate size (increase in mask size). The problem of flexure also causes the mixture of colors. In the extreme case, the organic layer is not formed in some regions. As a result, a defect occurs due to leakage between upper and lower electrodes. In addition, according to the conventional method, a mask deteriorates and becomes unusable after it is used specific times. Accordingly, the problems of an increase in mask size leads to an increase in cost of a display. Especially the cost problem is regarded as the biggest problem in an organic EL display.
In view of this, a method of producing a large-sized display by connecting a plurality of organic EL displays is proposed. However, in a case where a plurality of panels are connected, a seam is observed between the panels. This undesirably causes a decline in display quality. As a solution for this problem, Patent Literature 1 proposes a method of eliminating such a seam by sealing four panels from behind the panels at the sacrifice of an aperture ratio. Further, Non-Patent Literature 1 proposes a method of eliminating such a seam by disposing two panels so that sealing parts overlap each other and by bonding a transparent plate having an adjusted refractive index onto a substrate of one of the two panels.